Ambient fine particle matter (<2.5 |j,m in diameter [PM2.s]) is hypothesized to be a factor in the exacerbation of asthma. The current US EPA standard for fine particles may not protect a sensitive sub-group-children with asthma. Limitations in the few cross-sectional and panel studies of the health effects of particle exposure are numerous and include: small subject numbers, narrow range of asthma severity, narrow time frame of observation, no control for household characteristics and allergic status, limited information on particles (chemical speciation and sources), and poor control of gaseous co-pollutants. We recently completed a prospective, 1-year follow-up study of 466 physician-diagnosed asthmatic children residing in southern New England, a region that includes an area of non-attainment of the EPA standard. Preliminary analysis using data from our Childhood Asthma Study and using limited, publicly available data on chemical constituents of PM2.5, suggests that daily respiratory health is compromised by exposure to particular components of PM2.s. In this grant application, we propose to acquire and analyze the stored, fine-particle collection filters from EPA monitoring sites in our region for trace elements and elemental carbon. We further propose to take advantage of the 158,000 subject-days of symptom and medication use data from our Childhood Asthma Study to examine the impact of exposure to PM2.5 and PM2.5 constituents on respiratory health. The primary health outcomes are: mother-reported daily respiratory symptoms (wheeze, persistent cough, chest tightness and shortness of breath) and medication use;and monthly asthma severity, assessed using the Global Initiative for Asthma (GINA) guidelines. Associations will be assessed with longitudinal repeated measures analyses using generalized estimating equations as well as empirical Bayes methods that will take into account sources of variability of exposures. Gaseous co-pollutants, meteorological variables and potential confounders (season of the year, atopic status of the child, local traffic density) will also be included in the evaluation. Relevance: Results of this study will provide important information necessary to assess the adequacy of the EPA PM2.5 standard, could identify the component(s) of PM2.s having the strongest impact on respiratory health, and could lead to more cost-effective strategies for source-targeted air-pollution interventions.